Influence of cation site disorder in ZnGeN₂ on electronic properties

Cation disorder-dependent II-IV-V₂ materials show promise for tuning band gaps with lattice parameters matched to their analogue III-V semiconductors for use in energy-relevant devices such as LEDs and PV. Disorder-synthesis-property relationships for these materials are not well understood, but new computational techniques can provide information complementary to experimental investigations and reveal the underlying physics of these materials. Using a combination of first principles, cluster expansion, and Monte Carlo methods, we investigated cation disorder in ZnGeN₂ and its effect on electronic structure as a function of effective temperature. We identify an order-disorder transition at an effective temperature of 2500K (achievable using nonequilibrium synthesis), where the local environment of nitrogen changes from exclusively 2:2 Zn:Ge coordination to the inclusion of higher energy motifs. Since ordering is a complex effect with implications on multiple length scales, metrics for assessing ordering based on cation site occupancy are compared for disordered structures at effective temperatures above this transition. This study provides insight into the synthesis-property relationship for ZnGeN₂ and provides a point of comparison with other ternary semiconductor systems.